DTMF signals are employed within telecommunication systems to initiate calls, and facilitate control of certain services and/or equipment. The services and/or equipment may be both internal and external to the particular network facilitating a call. For example, codes called "triggers", comprised of one or more DTMF signals, allow network subscribers to control network-based services such as multi-party conferencing. Network subscribers may also need to transmit, via the network, DTMF triggers to equipment and services external to the network, such as answering machines and automated banking services.
Network subscribers have had little control as to the propagation of DTMF signals which they transmit, giving rise to a number of potential problems. For example, assume a network subscriber placed a call to a particular party via a network offering multi-party conferencing in response to a DTMF trigger received from the subscriber. During the course of the call, the conferencing feature allows a subscriber to instruct the network, via a transmitted DTMF trigger, to connect additional parties to the call. The transmitted DTMF trigger would be detected by network-based equipment which would perform the requested connection of the additional party or parties. Unfortunately, like any other audio band signal sent from the subscriber's telephone, the DTMF trigger would also be transmitted to the originally called party. Such audible signals would disrupt any communication with that first called party. For obvious reasons, such disruptions are undesirable.
Arbitrarily blocking all DTMF signals at some point within the network between the network-based equipment to which a network subscriber must transmit DTMF triggers, and the party with whom the subscriber is connected would prohibit DTMF signals from disrupting communications with that party. However, this blocking would also prevent a subscriber from transmitting DTMF triggers to equipment and services external to the network. Previously known network-based arrangements have provided for detecting and selectively blocking a limited number of unique triggers intended for equipment internal to a particular network, while allowing all other DTMF signals to propagate to parties/equipment external to the network. However, these arrangements are limited in their versatility, and cause unacceptable propagation delays within a network.